Shocking moment a teenager, 17, is hit by a speeding van before being thrown into a brick wall leaving him fighting for life

The shocking moment an alleged drug-addled driver mounts a footpath at high speed throwing a teenager 20m into a wall has been caught on dash-cam footage.

The 17-year-old boy was walking home from Casula train station with a friend when a grey Kia Carnival suddenly veered across two lanes of traffic on the Hume Highway and mounted the kerb at 12.40pm on Thursday.

With no warning and nowhere to run, the van can be seen smashing into the teen at high speed, with the exact moment of impact too distressing to show readers.

Dash-cam footage captured the moment, seconds before impact, that the two young men walked innocently up the footpath, not knowing that one of them would not make it home

After hitting the 17-year-old teenager the Kia van continued its path of destruction down the footpath, smashing fences, sign posts and thick wooden palings for more than 100m 

The boy was flung into the air travelling 20m into the side of a brick house, leaving him fighting for his life with critical head injuries along with lower leg and pelvic injuries.

The rear dash-cam footage shows the van continuing its path of destruction at high speed for more than 100m down the pedestrian footpath.

It can be seen smashing away fencing and sign posts outside the Jolly Knight Motel and narrowly avoiding power poles as it hurtled along the pavement mowing down several thick waist-high woo

The teenager was taken to Westmead hospital where he remains, fighting for his life. 

His friend was uninjured, having been narrowly missed by the van.  

The van slammed the teenage boy knocking him 20m to hit the brick wall of this house

The teenager was walking down the footpath with a friend when the van came out of nowhere, veering across two lanes to mount the kerb and hit him, leaving him in a critical condition

The Kia van continued along the pavement for more than 100m on the Hume Highway, Casula

Pictures taken at the scene showed the van with a smashed windshield and a large dent in the front with one of the headlights missing.

Images also showed debris including car pieces, bloodied clothing and an uprooted pole, scattered on the footpath. 

The incident caused chaos on the Hume Highway for hours.   

Police allege the driver, Cameron Forsyth, 37, of Leppington in Sydney's southwest, was impaired by morphine, heroin and cannabis at the time of the crash.

Debris was strewn across the footpath including a smashed power pole and blood-soaked clothes. An empty shoe can be seen on the grassy verge

There was traffic chaos on the Hume Highway for hours after as the road had to be closed for emergency responders and police investigators

Mr Forsyth was uninjured and taken to Liverpool hospital for drug and alcohol testing.

He appeared in Parramatta Local Court on Friday after being charged by Liverpool police with dangerous driving occasioning grievous bodily harm - drive in manner dangerous, and negligent driving occasioning grievous bodily harm.

His license was suspended and he was remanded in custody to next appear in court on March 8.